ios - How to move the object(tanker ) on slope image in chipmunk Spacemanager

I have used one polygon shape image (terrain)in my game its just like mountain and now i want to move the tanker on mountain path from one direction to other and then its turn on touching of the screne and move back and move like this continuously, i am not getting the method to move the tanker on slope(image) path in chipmunk spacemanager.

b.when collision detection happen like that if any bomb will fall on slope(image of mountain) then i want little damage on slope(image of mountain) like this video i want to please see this video for more details.

http://www.youtube.com/watch?v=vleq3Wa_jZs

i have used this code but my object(tanker) is following terrain path with rotation i want to just move like tanker moving and follow terrain path.

-(void)AddWheel
{
    cpShape *localPlayerShape;
    cpCCSprite *localPlayerSprite;

    localPlayerShape = [mySpaceManager  addCircleAt:[self GetStartingWheelPosition] mass:2 radius:7];

    localPlayerSprite = [cpCCSprite spriteWithFile:@"enemy1.png"];

    localPlayerSprite.shape=localPlayerShape;

    localPlayerSprite.shape->group=kItemIsPartOfTheTankGroup;
    localPlayerSprite.shape->collision_type=kItemIsPartOfTheTankGroup;

    localPlayerSprite.shape->u=4.5;

    localPlayerSprite.tag=100;


    [mySpriteLayer addChild:localPlayerSprite z:15];
}

Thank waiting for you all reply .